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2.20
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Observed changes in regional climate over the past
50 years have affected biological and hydrological systems in many parts
of the world (see Table 2-1).
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| 2.21 |
There has been a discernible
impact of regional climate change, particularly increases in temperature,
on biological systems in the 20th century. In many parts of the world
the observed changes in these systems3,
either anthropogenic or natural, are coherent across diverse localities
and are consistent in direction with the expected effects of regional changes
in temperature. The probability that the observed changes in the expected
direction (with no reference to magnitude) could occur by chance alone is
negligible. Such systems include, for example, species distributions, population
sizes, and the timing of reproduction or migration events. These observations
implicate regional climate change as a prominent contributing causal factor.
There have been observed changes in the types (e.g., fires, droughts, blowdowns),
intensity, and frequency of disturbances that are affected by regional climatic
change (either anthropogenic or natural) and land-use practices, and they
in turn affect the productivity of and species composition within an ecosystem,
particularly at high latitudes and high altitudes. Frequency of pests and
disease outbreaks have also changed, especially in forested systems, and
can be linked to changes in climate. In some regions of Africa, the combination
of regional climate changes (Sahelian drought) and anthropogenic stresses
has led to decreased cereal crop production since the year 1970. There are
some positive aspects of warming: For example, the growing season across
Europe has lengthened by about 11 days from the years 1959 to 1993, and
energy consumption for heating in winter has decreased.
|
WGII TAR Sections 5.4, 5.6.2,
10.1.3.2, 11.2,
13.1.3.1, & 13.2.4.1,
& WGII TAR Figure
SPM-1 |
| 2.22 |
Coral reefs are adversely
affected by rising sea surface temperatures. Increasing sea surface
temperatures have been recorded in much of the tropical oceans over the
past several decades. Many corals have undergone major, although often partially
reversible, bleaching episodes when sea surface temperatures rise by 1°C
in any one season, and extensive mortality occurs for a 3°C rise. This
typically occurs during El Niño events and is exacerbated by rising
sea surface temperatures. These bleaching events are often associated with
other stresses such as pollution.
|
WGI TAR Section 2.2.2.2 &
WGII TAR Sections 6.4.5
& 17.2.4.1 |
| 2.23 |
Changes in marine systems,
particularly fish populations, have been linked to large-scale climate oscillations.
The El Niño affects fisheries off the coasts of South America and
Africa and the decadal oscillations in the Pacific are linked to decline
of fisheries off the west coast of North America.
|
WGI TAR Section 2.6.3 &
WGII TAR Sections 10.2.2.2,
14.1.3, & 15.2.3.3 |
| 2.24 |
Changes in stream flow, floods,
and droughts have been observed. Evidence of regional climate change
impacts on elements of the hydrological cycle suggest that warmer temperatures
lead to intensification of the hydrological cycle. Peak stream flow has
shifted back from spring to late winter in large parts of eastern Europe,
European Russia, and North America in the last decades. The increasing frequency
of droughts and floods in some areas is related to variations in climate -- for
example, droughts in Sahel and in northeast and southern Brazil, and floods
in Colombia and northwest Peru. |
WGI TAR Section 2.7.3.3, WGII
TAR SPM, WGII TAR Sections
4.3.6, 10.2.1.2, 14.3,
& 19.2.2.1, &
WGII TAR Table 4-1 |
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